Highway construction zones and accidents are often a major source of congestion in highways as they interrupt the normal traffic flow due to temporarily restricting the available highway lanes. Reduction of the number of available traffic lanes and re-routing the traffic to improvised new traffic lanes cause conditions that are unexpected by the motorist.
To alleviate such congestion systems have been developed that advise the motorist well ahead of the construction or other incident zones of traffic problems ahead, and anticipated congestion and reduced speed requirements. Such systems may be either temporary, using free standing signaling devices such as remotely controllable traffic lights or variable message boards (VMS) in communication with a remote central controller together with movable roadside traffic flow sensors, or fixed using permanently installed variable message boards in combination with a remote controller and either permanent or temporary roadside traffic sensors. Roadside traffic flow sensors have been known to include occupancy detectors which detect vehicle flow interruption in a highway lane, traditional speed detectors and video cameras.
Typically such systems include a central control, usually located in the vicinity of the incident or construction zone but also possibly remote thereof. The central control is almost always a computer adapted to receive status information from different roadside devices and able to remotely control such devices so as to, in the case of a VMS for example, display messages to the motorists well ahead of the problem zone.
Communications between the central control and the roadside devices may be by hard wire connection, telephone link, or radio frequency transmitter/receiver (Transceiver). In such case, the roadside device and the central control include modems for communicating with each other.
“Advanced Portable Traffic Management System Work Zone Operational Test” by Nookala et al describes a highway safety system that incorporates the use of widespread spectrum radio, cellular phone and Integrated Services Digital Network (ISDN) phone links. The spread spectrum radio is used to link roadside nodes to the central control computer. The signal transfers from node to node, the nodes acting both as relay and a means of communication between nodes. Together with the ISDN link and cellular phone the system performs as part of an Ethernet network. Each remote terminal (roadside) is equipped with an Ethernet EHUB which allows multiple devices to share the Ethernet. The system includes establishment of a web page to provide traffic information accessible by motorists planning a trip through the Internet.
Thus there presently are known a number of sophisticated systems used in traffic control. However what these systems have in common is the sequential polling of the different roadside devices regardless of the communication mode adopted in the system. A much more efficient mode of communication would be the quasi-simultaneous polling of all devices particularly if such polling could be implemented in a continuous mode.